A time-controlled heat-triggered hydrophobic capsule and a method for preparing the same

Abstract

The application discloses a time-controlled thermal trigger hydrophobic capsule and a preparation method thereof. The capsule comprises a hydrophobic active substance, a thermal response matrix and a selective additive component. The hydrophobic active substance accounts for 30%-70% of the total mass of the capsule and comprises one or more of stearic acid, behenic acid or long-chain alkyl silane. The thermal response matrix is a waxy material with a melting point of 40-70 DEG C. The selective additive component comprises a mechanical reinforcing agent and an interface modifier. The preparation method comprises oil phase preparation, water phase preparation, shearing emulsification, ultrasonic refinement, cooling solidification and separation, and washing and drying. The application uses the hydration heat of the magnesium oxide solidification system itself as a trigger signal, ensures that the hydrophobic agent is released only after the main body of the carbonization reaction is basically completed, fundamentally solves the contradiction that the hydrophobic agent hinders the hydration carbonization, and greatly improves the ability of the solidified soil to resist water penetration and acid rain erosion through double protection.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering and engineering materials technology, and in particular to a time-controlled thermally triggered hydrophobic capsule for improving the impermeability and acid rain resistance of solidified soil and its preparation method. Background Technology

[0002] In recent years, the geotechnical engineering field has focused on developing various soil carbonation technologies. These technologies primarily utilize materials such as magnesium oxide and lime, along with some industrial byproducts and biological solidifying agents, to react with carbon dioxide and generate carbonate products that can replace cement. While this method effectively avoids the large carbon emissions generated during traditional cement production and use, and can further reduce emissions by absorbing carbon dioxide, demonstrating significant environmental benefits, engineering practice shows that magnesium oxide-stabilized soil faces two major challenges in actual service, limiting its long-term durability and widespread application.

[0003] Firstly, the soil lacks sufficient impermeability. The solidified soil contains micropores and original fissures, making it susceptible to water intrusion and structural damage under conditions such as rainfall and groundwater level fluctuations. More seriously, precipitation in industrial areas or regions prone to acid rain is acidic, and the intruding acid rain (whose main component is...) , Magnesium oxide (MgO) reacts with magnesium carbonate and incompletely carbonized magnesium hydroxide, leading to the decomposition of cementitious products, softening of soil structure, significant strength reduction, and even failure. Traditional methods for improving the impermeability of concrete or soil mainly rely on surface coatings (such as silane impregnating agents and organosilicon coatings) or the integral incorporation of water-repellent agents (such as stearates). However, surface coatings cannot repair internal damage and are difficult to apply in underground soil; while directly incorporating water-repellent agents severely hinders the early hydration and carbonation reactions of magnesium oxide, because the water-repellent agent encapsulates active MgO particles, isolating them from contact with water and carbon dioxide, resulting in insufficient solidification reaction and severely impaired strength development. Therefore, this invention aims to provide a novel material as a solution to the above problems, which can endow magnesium oxide-solidified soil with excellent overall hydrophobicity and acid rain resistance, while ensuring that its core solidification reaction is not disturbed. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a time-controlled thermally triggered hydrophobic capsule and its preparation method for improving the impermeability and acid rain resistance of solidified soil.

[0005] Technical Solution: The time-controlled thermally triggered hydrophobic capsule of the present invention comprises a hydrophobic active substance, a thermally responsive matrix, and selectively added components; the hydrophobic active substance accounts for 30%-70% of the total mass of the capsule, including one or more of stearic acid, behenic acid, or long-chain alkylsilanes; the thermally responsive matrix is ​​a waxy material with a melting point of 40℃-70℃, and the thermally responsive matrix and the hydrophobic active substance are screened and compounded to match the thermal triggering temperature with the peak temperature reached by the target magnesium oxide solidified soil mixture during the carbonization process; the selectively added components include mechanical reinforcing agents and interface modifiers.

[0006] Furthermore, the waxy material includes paraffin wax, beeswax, microcrystalline wax, Fischer-Tropsch wax, or stearic acid itself.

[0007] Furthermore, the peak temperature of the carbonization reaction is 70℃ - 80℃, and the thermal trigger temperature of the capsule is designed to be 55℃ - 65℃.

[0008] Furthermore, the mechanical reinforcing agent comprises 1% to 5% of low-density polyethylene powder or ethylene-vinyl acetate copolymer, which form micro-crosslinking points in the wax matrix.

[0009] Furthermore, the interface modifier includes 0.5% - 2% of a silane coupling agent to promote the chemical bonding between the released hydrophobic agent and the inorganic surface of the soil.

[0010] Furthermore, the amount of capsules added is 0.5% - 3.0% of the total dry soil mass in the solidified soil.

[0011] The preparation method of the time-controlled thermally triggered hydrophobic capsule of the present invention includes the following steps:

[0012] Step 1: Oil phase preparation. Place the mixture in a reaction vessel, heat to 75℃-85℃, and continuously stir mechanically under inert gas protection until a completely transparent and homogeneous melt blend is formed, which is the oil phase.

[0013] Step 2: Aqueous phase preparation. In another container, dissolve 0.5% - 3% of the emulsifier by mass in deionized water preheated to 75°C - 85°C, and stir thoroughly to dissolve. This is the aqueous phase.

[0014] Step 3: Shear emulsification. Under the continuous operation of the high-speed shear mixer, the hot oil phase prepared in step 1 is slowly and dropwise added to the hot water phase in step 2. After the addition is completed, high-speed shearing continues for 5-10 minutes to form a preliminary oil / water type crude emulsion.

[0015] Step 4: Ultrasonic refining. The crude emulsion from Step 3 is transferred to an ultrasonic treatment tank and subjected to ultrasonic crushing at a constant temperature of 75℃ - 80℃.

[0016] Step 5: Cooling, solidification and separation. Transfer the microemulsion to a container with slow stirring and control it to cool slowly to room temperature at a rate of 0.5 - 2℃ / min.

[0017] Step 6: Washing and drying. Wash the collected microspheres 2-3 times with cold deionized water and anhydrous ethanol in sequence. Place the washed wet capsules in a drying oven below 40℃ and dry for 6-12 hours to obtain free-flowing powdered time-controlled thermally triggered hydrophobic capsules.

[0018] Furthermore, in step 4, the ultrasonic power is set to 300-500W, a pulse mode is used, and the total processing time is 3-8 minutes, until the emulsion droplet size distribution is uniform and the average particle size reaches 10-100 micrometers, forming a fine microemulsion.

[0019] Furthermore, in step 5, the oil phase inside the emulsion droplets gradually solidifies to form solid microspheres, which are then collected by vacuum filtration or centrifugation.

[0020] Furthermore, in step 5, the stirring speed of the slow stirring container is 200-400 rpm.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0022] (1) Intelligent triggering without interfering with the core reaction: The heat of hydration of the magnesium oxide curing system itself is used as the trigger signal to ensure that the hydrophobic agent is released only after the carbonization reaction is basically completed, which fundamentally solves the contradiction that the hydrophobic agent hinders hydration and carbonization.

[0023] (2) Dual protection, significantly improved durability: It realizes a dual protection mechanism that combines "overall prevention during the maintenance period" and "partial repair during the service period", which greatly improves the ability of solidified soil to resist water penetration and acid rain erosion;

[0024] (3) Simple construction and wide applicability: As a solid powder additive, the capsule can be added at one time during the mixing stage. The construction process is completely consistent with the traditional solidified soil. No additional equipment or complex process is required. It is especially suitable for scenarios where traditional surface protection is difficult to implement, such as underground, underwater, and irregular structures.

[0025] (4) Balance between strength and functionality: The capsules have a low dosage and are micron-sized particles, which have little effect on the final mechanical strength of the solidified soil. They achieve a qualitative leap in durability by sacrificing very little strength. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the working principle of a time-controlled thermally triggered hydrophobic capsule.

[0027] Figure 2 This is a flowchart illustrating the preparation process of time-controlled thermally triggered hydrophobic capsules. Detailed Implementation

[0028] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0029] The time-controlled thermally triggered hydrophobic capsule of the present invention comprises hydrophobic active substances, thermally responsive matrix and selectively added components weighed in a predetermined ratio.

[0030] The main components of the hydrophobic active substance are selected from one or more of stearic acid (octadecanoic acid), behenic acid (docosahexaenoic acid), or long-chain alkylsilanes (such as octadecyltrimethoxysilane). Its function is to reduce the surface energy of the material and impart hydrophobicity to the solidified soil by physically adsorbing or chemically bonding with the surface of newly formed magnesium carbonate and other products in the soil after release. Mass percentage: 30% - 70% of the total capsule mass, to balance hydrophobic performance with the structural strength of the capsule.

[0031] The main components of the thermally responsive matrix are waxy materials selected from those with melting points in the range of 40℃-70℃, including but not limited to paraffin wax (melting point 48-62℃), beeswax, microcrystalline wax, Fischer-Tropsch wax, or stearic acid itself (when used as part of the thermally responsive matrix). Its core function is to lower the melting point of the mixture with the hydrophobic agent, causing a phase transition at a specific temperature. A key characteristic is that the waxy materials and hydrophobic active substances must be precisely screened and compounded to ensure that their thermal trigger temperature matches the peak temperature reached internally during the carbonization process of the target magnesium oxide-stabilized soil mixture. Typically, the peak temperature of the carbonization reaction can reach 70℃-80℃, and the capsule thermal trigger temperature is designed to be 55℃-65℃.

[0032] Selective additives include: Mechanical reinforcing agents: To improve the survival rate of the capsules during mixing, 1%-5% of low-density polyethylene (LDPE) powder or ethylene-vinyl acetate copolymer (EVA) can be added to the compound. These polymers can form micro-crosslinking points in the wax matrix, improving the abrasion resistance and compressive strength of the capsules; Interface modifiers: Adding 0.5%-2% of silane coupling agents (such as γ-(2,3-epoxypropoxy)propyltrimethoxysilane) can promote the interaction between the released hydrophobic agent and the inorganic surface of the soil (such as...). , Chemical bonds of ).

[0033] The time-controlled hydrophobic capsules prepared above were used as functional additives in magnesium oxide-stabilized soil. The amount of capsules added was 0.5% - 3.0% of the total dry soil mass in the stabilized soil. The time-controlled thermally triggered hydrophobic capsules, magnesium oxide, soil, and required water were uniformly mixed in one go using conventional mechanical mixing methods. After the mixture was filled, a carbonization process was carried out. The internal temperature of the soil continued to rise. When the internal temperature rose to equal or higher than the thermal trigger temperature of the capsules, the capsules underwent a melting phase transition, and their microstructure changed from a dense solid to a permeable liquid network. The hydrophobic active substances then gained fluidity and were released and diffused. The liquid hydrophobic agent spread on the surface of the newly formed pore network of the soil and the cementing products (magnesium hydroxide and magnesium carbonate generated by subsequent carbonization) through capillary action. The carboxyl groups (-COOH) of carboxylic acid hydrophobic agents such as stearic acid can react with magnesium ions on the surface of the cementing products. Chemical adsorption or reaction occurs, forming a robust hydrophobic monolayer. Subsequent liquid water or acid rain intruding into the soil cannot wet the hydrophobic pores and particle surfaces, thus greatly inhibiting capillary absorption and infiltration rates. Hydrogen ions in the acid also have difficulty contacting the cementitious products protected by the hydrophobic layer, thereby significantly improving the long-term durability of the solidified soil from both physical and chemical perspectives.

[0034] Chemical reaction equation:

[0035] Taking stearic acid as an example, its interaction with the surface of the gelled product is as follows:

[0036]

[0037] More specifically, it reacts with the magnesium phase:

[0038]

[0039] This reaction demonstrates that the hydrophobic agent is firmly anchored to the soil skeleton through chemical bonding, forming a durable hydrophobic layer. The small amount of water or hydrogen ions generated in the reaction can be buffered or diffused by the system.

[0040] like Figure 1 The diagram shows the working principle of the time-controlled thermally triggered hydrophobic capsule. The two sides of the diagram are soil particles, and the middle is the pores between the particles. The white particles in the upper diagram are magnesium oxide, the pink particles are the capsule described in this application, and the light yellow particles in the lower diagram are magnesium carbonate. In (a), when the capsule is mixed in, the hydrophobic agent will not wrap the magnesium oxide and will leave pores so that the hydration and carbonation reactions of magnesium oxide can proceed normally. In (b), as the hydration and carbonation reactions of magnesium oxide proceed and are basically completed, the soil temperature rises to the melting point of the capsule, the hydrophobic agent melts and wraps the magnesium carbonate, reacts and fills the pores.

[0041] like Figure 2 As shown, the preparation method of the time-controlled thermally triggered hydrophobic capsule of the present invention includes the following steps:

[0042] Step 1: Place the mixture in a reaction vessel and heat it to 75℃-85℃ (i.e., about 10-15℃ higher than the highest melting point component). Under the protection of an inert gas (such as nitrogen), continue to stir mechanically (to prevent thermal oxidative decomposition of stearic acid) until a completely transparent and homogeneous melt blend is formed as the oil phase.

[0043] Step 2: Aqueous phase preparation. In another container, dissolve 0.5% - 3% by mass of emulsifier (preferably a nonionic emulsifier, such as Tween-80 or Span-80) in deionized water preheated to 75°C - 85°C, and stir thoroughly to dissolve, thus forming the aqueous phase.

[0044] Step 3: Shear emulsification. Under continuous operation of a high-speed shear mixer (8000-12000 rpm), the hot oil phase prepared in Step 1 is slowly and dropwise added to the hot water phase in Step 2. After the addition is complete, continue high-speed shearing for 5-10 minutes to form a preliminary oil / water-based crude emulsion.

[0045] Step 4: Ultrasonic Refinement. Transfer the coarse emulsion from Step 3 to an ultrasonic treatment tank and perform ultrasonic fragmentation at a constant temperature of 75℃-80℃. Set the ultrasonic power to 300-500W, using pulse mode (2 seconds on, 2 seconds off), for a total processing time of 3-8 minutes, until the emulsion droplets are uniformly distributed and the average particle size reaches 10-100 micrometers, forming a fine microemulsion.

[0046] Step 5: Cooling, solidification, and separation. Transfer the microemulsion to a container with slow stirring (200-400 rpm) and slowly cool it to room temperature (approximately 25°C) at a rate of 0.5-2°C / min. During this process, the oil phase inside the emulsion droplets gradually solidifies, forming solid microspheres. Collect the solid microspheres by vacuum filtration or centrifugation.

[0047] Step 6: Washing and drying. Wash the collected microspheres 2-3 times sequentially with cold deionized water and anhydrous ethanol to thoroughly remove residual emulsifier from the surface. Place the washed wet capsules in a drying oven at below 40°C and dry for 6-12 hours to obtain free-flowing, powdered, time-controlled thermally triggered hydrophobic capsules.

Claims

1. A time-controlled thermally triggered hydrophobic capsule, characterized in that, It includes hydrophobic active substances, a thermally responsive matrix, and selectively added components; the hydrophobic active substances account for 30%-70% of the total mass of the capsule, including one or more of stearic acid, behenic acid, or long-chain alkylsilanes; the thermally responsive matrix is ​​a waxy material with a melting point of 40℃-70℃, and the thermally responsive matrix and the hydrophobic active substances are screened and compounded to match the thermal trigger temperature of the target magnesium oxide solidified soil mixture with the peak temperature reached by the internal temperature rise during the carbonization process; the selectively added components include mechanical reinforcing agents and interface modifiers.

2. The time-controlled thermally triggered hydrophobic capsule according to claim 1, characterized in that, The waxy material includes paraffin wax, beeswax, microcrystalline wax, Fischer-Tropsch wax, or stearic acid itself.

3. The time-controlled thermally triggered hydrophobic capsule according to claim 1, characterized in that, The peak temperature of the carbonization reaction is 70℃ - 80℃, and the thermal trigger temperature of the capsule is designed to be 55℃ - 65℃.

4. The time-controlled thermally triggered hydrophobic capsule according to claim 1, characterized in that, The mechanical reinforcing agent comprises 1%-5% low-density polyethylene powder or ethylene-vinyl acetate copolymer, which form micro-crosslinking points in the wax matrix.

5. The time-controlled thermally triggered hydrophobic capsule according to claim 1, characterized in that, The interface modifier includes 0.5%-2% silane coupling agent, which promotes the chemical bonding between the released hydrophobic agent and the inorganic surface of the soil.

6. The time-controlled thermally triggered hydrophobic capsule according to claim 1, characterized in that, The amount of capsules added is 0.5% - 3.0% of the total dry soil mass in the solidified soil.

7. A method for preparing a time-controlled thermally triggered hydrophobic capsule, characterized in that, Includes the following steps: Step 1: Oil phase preparation. Place the mixture in a reaction vessel, heat to 75℃-85℃, and continuously stir mechanically under inert gas protection until a completely transparent and homogeneous melt blend is formed, which is the oil phase. Step 2: Aqueous phase preparation. In another container, dissolve 0.5% - 3% of the emulsifier by mass in deionized water preheated to 75℃ - 85℃, and stir thoroughly to dissolve, thus forming the aqueous phase. Step 3: Shear emulsification. Under the continuous operation of the high-speed shear mixer, the hot oil phase prepared in step 1 is slowly and dropwise added to the hot water phase in step 2. After the addition is completed, high-speed shearing continues for 5-10 minutes to form a preliminary oil / water type crude emulsion. Step 4: Ultrasonic refining. The crude emulsion from Step 3 is transferred to an ultrasonic treatment tank and subjected to ultrasonic crushing at a constant temperature of 75℃ - 80℃. Step 5: Cooling, solidification and separation. Transfer the microemulsion to a container with slow stirring and control it to cool slowly to room temperature at a rate of 0.5 - 2℃ / min. Step 6: Washing and drying. Wash the collected microspheres 2-3 times with cold deionized water and anhydrous ethanol in sequence. Place the washed wet capsules in a drying oven below 40℃ and dry for 6-12 hours to obtain free-flowing powdered time-controlled thermally triggered hydrophobic capsules.

8. The method for preparing the time-controlled thermally triggered hydrophobic capsule according to claim 7, characterized in that, In step 4, the ultrasonic power is set to 300-500W, and a pulse mode is used. The total processing time is 3-8 minutes until the emulsion droplet size distribution is uniform and the average particle size reaches 10-100 micrometers, forming a fine microemulsion.

9. The method for preparing the time-controlled thermally triggered hydrophobic capsule according to claim 7, characterized in that, In step 5, the oil phase inside the emulsion droplets gradually solidifies to form solid microspheres, which are then collected by vacuum filtration or centrifugation.

10. The method for preparing the time-controlled thermally triggered hydrophobic capsule according to claim 7, characterized in that, The stirring speed of the slow stirring container in step 5 is 200-400 rpm.

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